1. Field of the Invention
The present invention relates to electronic apparatus for generating data for determining properties of gemstones, such as cut diamonds. In particular, but not exclusively, it relates to electronic apparatus for generating data for determining properties of gemstones in which a plurality of images of the gemstone are captured for analysis under different lighting conditions.
2. Description of the Related Technology
The beauty of a gemstone, such as a cut diamond, derives from its light handling ability. What attracts the eye is the “game of light” played by a well-cut diamond as incident light is reflected and refracted off its many facets. Diamonds and other gemstones may be cut according to many different standardised cut patterns such as the standard round brilliant cut, oval, pear, marquise, radiant, princess, heart, emerald cut etc. The most popular cut is the standard round brilliant (SRB) cut as shown in FIG. 1. Diamond cutting and polishing is a highly skilled art and a well-cut diamond, having superior optical performance, will command a significant price premium over a poorly cut diamond having inferior optical performance.
When showing a cut diamond to an untrained observer, one frequently refers to the four C's of a gemstone, being its carat weight, its clarity, its cut and its color. Carat weight, clarity and color can be relatively easily measured objectively and are therefore generally useful. Cut may also be specified or measured in terms of the geometry of the various facets. However, what really matters is the light handling ability of the gemstone and reference is often made to more subjective parameters of a cut diamond, such as its brilliance (the intensity of light returned), scintillation (fast and local fluctuations in the light returned as the diamond moves relative to the lighting conditions), fire (the dispersion of white light into spectral colors) and symmetry (the symmetry of light patterns such as the so-called “hearts and arrows”). It can be difficult, particularly for an untrained observer, to make a personal appraisal of these subjective parameters. It can also be difficult to compare the light handling abilities of two diamonds with the same carat weight, clarity and color, and therefore to appreciate why one is more valuable than the other.
It is recognized that properties such as brilliance, fire and symmetry should be derived, whether by experimental observation or theoretical computer modelling, under a variety of lighting conditions. Moreover, with the property of scintillation it is clearly essential to observe or model the diamond under a variety of lighting conditions. Electronic apparatus for capturing images of gemstones under varying lighting conditions for analysis are known.
The present applicant previously filed a European patent application EP 1319942 for an apparatus designed to measure properties of a gemstone. In this application, it is described that properties of a gemstone are determined by capturing images of a gemstone at a number of rotational positions relative to a spatially varied light pattern. The spatially varied light pattern is produced by a reflector with two regions, one relatively reflective, and the other relatively non-reflective. The boundary between the two regions lies in a plane parallel to the axis along which observation of the gemstone takes place. That is, the length of the boundary between the two regions is at a minimum length, and is formed by a straight line from the centre of the reflector, through which the gemstone is observed, to its closest edge.
International Patent Publication number WO 96/23207 describes a device which captures color images of a gemstone placed in an analysis chamber and illuminated by a uniform annular light which may be moved along an axis such that the gemstone may be illuminated from a plurality of different angles. The device performs a spectral analysis of the captured images using a tuneable optical band pass filter to determine the color of the gemstone. Digital images of the gemstone may also be stored, displayed or transmitted over a data network.
The website (www.gemex.com) of GemEx Systems, Inc, a U.S. company, describes a device called the BrillianceScope Analyser which is described as an imaging spectrophotometer. Color images of a diamond are captured in a controlled lighting environment consisting of six lighting angles, five of which provide reflected light and one of which provides diffuse lighting. These images may then be analysed to generate a report on the diamond. The BrillianceScope Analyser device operates on the same principle as the device described in International Patent Publication number WO 96/23207 referred to above, in that the gemstone is placed in an analysis chamber and illuminated by a uniform annular light which may be moved along an axis such that the gemstone is illuminated from different angles. The images may be analysed by a computer, and the properties of “white light”, “colored light” and “scintillation” for a diamond are determined and displayed on three line chart scales from ‘low’, to ‘medium’ to ‘high’. Captured images may also be shown in a repeating sequence in one display area, giving the effect of light movement. Images of two gemstones may be displayed side-by-side for comparison.
International Patent Publication number WO 99/61890 describes a system for the standardised grading of gemstones. A gemstone is subject to a plurality of incident light sources and images are captured for analysis. Images of the gemstone, such as a SRB cut diamond, may be captured from various viewpoints such as from the pavilion, from the crown and side-on. The gemstone is supported by a rotatable platform which is rotated when images are being captured from a side-on viewpoint to obtain profile and color images from a variety of rotational positions and to detect internal flaws and inclusions. When capturing images from above and below the gemstone, the platform is moved along an axis from a level position to a down and an up position respectively. The fixed focal length camera is also moved along an axis to focus on the gemstone when the platform is moved between the up, down and level positions. A captured image may be analysed by a processor to obtain color measurements and measures of the brilliance and scintillation of the gemstone.
U.S. Pat. No. 4,900,147 describes a method and apparatus for mapping the crystalline structure of a diamond using Roman spectroscopy.
U.S. Pat. No. 2,332,755 describes a branding viewer for displaying a brand mark or a portion of a surface of a diamond.